Scalable coding is a technology that encodes a multimedia signal in a scalable manner so that various representations of the content can be extracted from a single codestream to fit a wide range of applications. Many scalable coders have been proposed and some have been adopted as standards. JPEG 2000 (J2K) is a scalable wavelet-based image-coding standard that supports resolution, quality, and color-component scalabilities within a single codestream. MPEG-4 Fine Granularity Scalability (FGS) is a fine-grain scalable video coding standard that supports both temporal and quality scalabilities. The recent Universal Scalable Video Coding (USVC) proposal supports temporal, spatial, and quality scalabilities (F. Wu, S. Li, R. Yan, X. Sun, and Y. Zhang, “Efficient and Universal Scalable Video Coding,” IEEE Int. Conf. Image Processing, September 2002, vol. 2, pp. 37-40). Embedded Audio Coding (EAC) supports quality, sampling-rate, and channel scalabilities (J. Li, “Embedded Audio Coding (EAC) with Implicit Auditory Masking,” Proc. 10th ACM Int. Conf. Multimedia, December 2002, pp. 592-601).
Scalable codestreams are usually organized upon fundamental building blocks denoted as “scalable building blocks” (SBBs). For example, a J2K encoder partitions a codestream according to tiles, components, resolution levels, precincts, and layers. Thus, a J2K SBB is a type of data packet that can be uniquely identified by the aforementioned scalable parameters. Based on supported scalabilities, SBBs can be extracted from a codestream and accessed for use by any one of the scalable parameters to form a best-fit representation for an application. SBBs also have an advantage that they can be truncated or rate-shaped. The “compression-once-decompression-many-ways” characteristic of SBBs is very desirable in many applications.
Multimedia Digital Rights Management (DRM) seeks to manage ownership and distribution rights for multimedia content from its creation to its consumption. MPEG-4 has been actively developing a DRM standard, the Intellectual Property Management and Protection (IPMP) protocol. Several commercial DRM products are also currently available, such as MICROSOFT® WINDOWS MEDIA® RIGHTS MANAGER (WMRM) (Microsoft Corporation, Redmond, Wa.). A DRM system such as WMRM encrypts and packages digital media content into a digital media file for super-distribution. A decryption key can be uploaded to a license server along with a specification of license rights selected by the publisher. To play protected content, a user first acquires a license from the proper license server that contains the decryption key and user access rights. A license to use the content is individualized and typically encrypted in such a way that the key binds to the user's hardware, making it impossible for the license to be used by others illegally.
While there are many encryption algorithms proposed for non-scalable multimedia formats, few are designed specifically for scalable multimedia formats. Wee, et al., propose a secure scalable streaming (SSS) schema that enables transcoding without decryption. (S. J. Wee and J. G. Apostolopoulos, “Secure Scalable Streaming Enabling Transcoding Without Decryption,” IEEE Int. Conf. Image Processing, 2001, vol. 1, pp. 437-440.) For MPEG-4 FGS, the approach encrypts video data in both base and enhancement layers except header data. Markers for RD-optimal (rate distortion-optimal) cutoff points have to be inserted into the unencrypted header for a middle stage to perform RD-optimal bit rate reduction. With regard to SSS, encryption granularity depends on the way a video stream is packetized. More precisely, encryption is applied to each packet. No modification on the packet size is allowed after encryption is done. SSS protects scalable media as a single access layer.
Grosbois et al. propose a simple layered access control schema for the image compression standard of JPEG 2000. (Raphael Grosbois, Pierre Gergelot, and Touradj Ebrahimi, “Authentication and Access Control in the JPEG 2000 compressed domain,” Proc. of SPIE 46th Annual Meeting, Applications of Digital Image Processing XXIV, San Diego, 2001.) In this scheme, a J2K image codestream is divided into two layers: the unencrypted layer and the encrypted layer. For the access control on resolution, the scheme pseudo-randomly flips the signs of the wavelet coefficients in the high frequency subbands. For the access control on layers, the bits in the codewords of the coding-passes belonging to last layers are pseudo-randomly flipped. Both types of access controls cannot be supported simultaneously.